1. Technical Field
The present invention relates to an image display system, an image display apparatus, and an image correction processing program.
2. Related Art
Projectors have been known as image display apparatuses.
There has been known a projection system, serving as an image display system including a personal computer serving as an information processing apparatus for correcting the shape and color of an image source, a projector for projecting the image corrected by the personal computer on the a screen, and a UBS cable serving as a data transmitting path between the personal computer and the projector (for example, see JP-A-2004-69996). In the projection system, the image source input to the personal computer is processed by an image processing unit of the personal computer. The image correcting processes include, for example, a keystone correcting process for correction keystone distortion caused by the arrangement relationship between the projector and the screen, a γ correcting process or a VT-γ correcting process for correcting colors on the basis of output characteristics of the projector, a color correcting process for correcting brightness irregularity or color irregularity due to characteristics of a liquid crystal panel, and a ghost correcting process or a cross talk correcting process for correcting color irregularity (ghost or cross talk) caused by the effect of a driving signal on adjacent pixels when pixels of the liquid crystal panel are driven. The image data corrected by the personal computer is transmitted to the projector via the signal transmitting member. The projector projects the transmitted image data onto the screen to display a predetermined image on the screen.
According to the above-mentioned structure, the personal computer mainly performs the image processing, and the projector just projects the image data onto the screen, so that image processing can be easily performed. Therefore, the above-mentioned structure makes it possible to simplify the configuration of the projector. In addition, since the personal computer has a graphic processing function, the personal computer can perform a high-accuracy image correcting process without adding new functions.
In a case in which the image source is a moving picture, when the transmission rate of the USB cable is low, it takes a lot of time to transmit one image data, and thus the frame rate of the images displayed by the projector is lowered, which causes the moving picture not to be appropriately reproduced. For example, a frame rate of 30 frames per second is needed to smoothly reproduce the moving picture. However, a USB 2.0 cable has an insufficient frame rate to transmit all image data. For example, a maximum stable communication speed of the USB 2.0 cable is about 240 Mbps, but in a display resolution of XGA (1024×768 dots), an image having pixels each having color information of 30 bits has data of about 25 Mbits. Therefore, image data is transmitted only at a frame rate of about 9 frames per second, which is a low frame rate.
JP-A-2004-69996 discloses a technique for reducing the amount of necessary transmission data by “transmitting differential data of previous screen data” and thus for keeping the frame rate at an appropriate level (see paragraph [0048] of JP-A-2004-69996). In JP-A-2004-69996, a personal computer generates differential data and transmits the differential data to a projector. Then, the projector synthesizes the received differential data with the previous screen to generate the current frame data, and projects the current frame data onto the screen.
When the personal computer performs all correcting processes on each image data, the image data is corrected to high-resolution image data, but the correcting processes are performed on most of the pixels of the image data. Then, even when the differential data between the previous image data and the current image data is obtained to reduce the amount of data transmitted from the personal computer to the projector, most of the pixels vary due to the previous image data and the current image data.
Therefore, even when the differential data is used, a data compression ratio is lowered, which causes a large amount of transmission data to be transmitted from the personal computer to the projector. As a result, data transmission from the personal computer to the projector is delayed, which causes a problem in that the frame rate of images displayed by the projector is not appropriately kept at a predetermined level.
For this reason, it is considered to lower the degree of image correction such that the differential data is not excessively large, but this is not preferable because the display quality of an image is deteriorated. When rough differential data is obtained such that a minute variation between image frames is not detected when the differential data is obtained, the size of the differential data can be reduced. However, in this case, information may be omitted from the current image data reproduced by the projector. Therefore, this method is also not preferable because the display quality of an image is lowered.